Adventures in Backup – continued

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Two weeks ago I discussed some bad experiences I had with Hyper-V + backup.  Since then I have spent a bunch of time setting up Hyper-V + backup on a couple of systems – and none were as problematic as my first attempt.  I have also setup my home Hyper-V server to perform nightly backups – which have been proceeding without a hick up:


However a lot of you let me know that you too had seen issues with backup and Hyper-V.  As such I would like to invite anyone who sees a failed Hyper-V backup to come here and let me know in the comments what the cause of the failure was – you can usually figure this out by looking in the Hyper-V event log (as I did in my original blog) – so that we can try to help each other out here.


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  • I was able to resolve some of my problems as well. Turns aout some of the servers were failing simply because I had the acronis true image agent installed. I tried removing it after a kb led me to using vssadmin list providers and in addition to the Microsoft vss I also had acronis hw vss.  The wierd part: I have that installed on other vm servers with no probs.  As of now I have one server that still fails but the local vm generates no error logs just alot of successful info events about SQL backing up.  That server does backup fine if shutdown though. May just go that route.

  • Ben,

    How can I best manage a backup of VMs on Hyper-V Servers' that are part of a cluster with CSV? Obviously I can simply backup from inside the guests, but is there a better way?


  • I've had mixed results with backing up Hyper-V VMs from the host, and I've come to the conclusion that under some circumstances (not sure what they are exactly) there's a bug with VSS on the host which causes the host's registry to balloon. A symptom of this is a lockup of the host after rebooting while the registry is being processed (the guest VMs can be running fine).

    If you get this issue, you will see it regardless of which backup product you use, (e.g. WSB, DPM, BackupExec, etc) because they all depend on VSS.

    This thread has a good description of the issue:

    Basically every VSS snapshot swells the registry. This can quickly be a problem if you have many VMs and are doing backups every 30 mins.

    I'm working with two new servers with this problem on R2 (with R2 VMs), they can lock up for 2 hours after a reboot. Yet I have an old server running 2008 RTM, with 2 VMs, doing backups every 30mins for over a year and reboots every 1-2 months, with no issue.

  • Ben, I've emailed you about a bug in Hyper-V via your contact form. I work with Aitor (from previous comment). Our new servers have over 24,000 VSS Snapshot devices in the registry which increase after every backup! Hyper-V is not deleting them from the host's registry which causes it to freeze after each reboot. We are not running any 3rd party software and it's a standard 2008 R2 Datacenter install on both machines.

  • Fixed that last server today (had a run of luck I guess) I had to uninstall integration services and then reinstall. Working great now.  Early I had tried updating that Host to SP2 and reinstalling integration services, but maybe I need a full uninstall of them for it to work.  I had also tried a couple of the VSS patches out there to no avail.

  • Well Ben, I just found your blog and love it. I know it will prove to be invaluable to me as I attempt to learn my way around Hyper-V and Server 2008. I teach at Lower Columbia College and am using both for the first time this year. I am trying to stay a page ahead of the students!

    Thanks for your tips and ideas and help.


  • Whoa! I started checking my Hyper-v servers and I too have a boat load of registry entries for SCSI devices.  What is the correct procedure to remove them?

  • Zac, how many devices are there in the registry and how big is your System hive file? Look in windows\system32\config\.

    There are two tools that could remove device entries from the reg. One is called Device Remover:

    And the other is a tiny tool that a MS engineer sent me called devnodeclean which removes phantom devices. It took 4 hours to remove 28,000 devices from our reg!

  • Could you upload anywhere this devnodeclean tool?

  • What about

    Volume Shadow Copy Service error: Unexpected error calling routine ConvertStringSidToSid.  hr = 0x80070539.


      OnIdentify event

      Gathering Writer Data


      Execution Context: Shadow Copy Optimization Writer

      Writer Class Id: {4dc3bdd4-ab48-4d07-adb0-3bee2926fd7f}

      Writer Name: Shadow Copy Optimization Writer

      Writer Instance ID: {e0f92a9e-0ee7-41a0-a307-1a7b2e9918de}

    When trying a backup of the host?

  • Any official word on the rapidly filling registry?

  • backing up hyperv is tough. to me it doesn't make sense to backup a virtual machine internally. using shadow copies on the host doesn't really work that well either. to really back them up you have to shut the machine down and do an export. seems kinda silly there's got to be a better way. really one should be able to export a live machine.

  • I am checking this daily for some official word about this registry issue. Ben, do you think it's safe to use these tools on production servers?  

  • this error appeared on my w7 ultimate 64bit after loading virtual clone drive. using their de-install doesn't help! virtual clone drive leaves stuff in the registry as well as on disk. some of which I haven't been able to delete yet.

    the error appears opeining up disk mgmt as well as with a backup product i am beta testing. possibly whenever vss is called.

    don't know if this helps the discussion.

  • Unexpected failure. Error code: 490@01010004

    sorry. I had put this in for title and it got overwritten.

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Adventures in Backup – continued